This invention relates to a secondary battery comprised of three polymer film sheets. One sheet contains an electrolyte and the other two sheets contain electrochemical species which may be in an anodic or a cathodic state depending upon whether the battery is discharging or is being charged.
A secondary battery is most simply defined as a battery which can be recharged. This recharge capability is due to the incorporation, within the battery, of electrochemical reactants which undergo a highly reversible electrochemical reaction to convert chemical energy to electrical energy upon discharge of the battery. Recharging of the battery converts electrical energy to chemical energy. The electrochemical reactants can be identified as electrochemical species having either an anodic or cathodic state depending upon whether the battery is in the discharge or the recharge mode. The anodic state is identified with the oxidation half of the electrochemical reaction, while the cathodic state is identified with the reduction half of the electrochemical reaction.
During the discharge mode, the battery acts as a voltage device in which the difference in the electrochemical potential between its anodic electrochemical species and its cathodic electrochemical species serves as a driving force to supply electrons through a load connected to the battery. The electrons produced by oxidation of the anodic electrochemical species pass from the battery's positive electrode, through the load and on to the battery's negative electrode. The battery's negative electrode is in association with the cathodic electrochemical species. The acceptance of electrons by the negative electrode results in reduction of the cathodic electrochemical species. When the potential difference between the battery's electrodes approaches zero volts, the source of electrons is substantially exhausted and the battery needs to be recharged.
During the recharge mode, the secondary battery behaves as an electrolysis device in which electrical energy is applied to the battery to provide the necessary electrons to convert the applied electrical energy into stored chemical energy. The electrochemical species, which was anodic and served as a source of electrons during discharge, becomes cathodic during recharge and accepts electrons. The electrochemical species which was cathodic during discharge becomes anodic during recharge. Although the roles of the battery's electrodes, i.e., the acceptance or the discharge of electrons, depends upon whether the battery is in the recharge or discharge mode, the positive electrode is always connected to the positive lead of the load. Similarly, the negative electrode is always connected to the negative lead.
Common secondary batteries are the alkaline and lead-acid batteries. These two types of batteries usually provide rigid cases in which the electrochemical species are contained. Due to the requirements of the materials of construction, these batteries can have considerable thicknesses and weights. This is especially true of the lead-acid battery.
In an attempt to reduce the dimensions of secondary batteries, recent battery research has turned to the use of polymeric films in secondary batteries. See European Patent Application No. 84107618.5, June 30, 1984. The use of polymeric films can provide batteries having very thin cross-sections and decreased weight.
It is therefore an object of this invention to provide a novel secondary battery which incorporates the utilization of polymeric films and which, as a result, has a very thin cross-section even when constructed of a plurality of cells. It is also an object of this invention to provide a secondary battery which has substantial flexibility.